The present disclosure is related to the field of preforming and resin infusion manufacturing of structural composite components.
In recent years, the aerospace and automotive industries showed increasing levels of interest in the application of resin infusion processes to manufacture structural components.
Dry, flexible and pre-formable fibrous products can in fact have significant advantages over standard pre-pregged materials due their longer shelf life and applicability to more complex geometries and around narrow radii.
The aspects of interdependence and criticality of the materials selection and processing stages are of special significance in automated lay-down/infusion processes wherein the stages of fiber placement, preforming and resin injection are distinct in phase, but coupled in materials selection and processing related aspects.
Sizings and binders can in fact simultaneously affect processing and thermo-mechanical performance of composite structures.
Composites cure kinetics and thermo-mechanical properties can be in fact influenced by the formation of an interface region between the fibrous component and the hosting matrix. In addition fiber/sizing/resin interactions occurring during the infusion stage can affect wet-out and local flow behavior through the development of stoichiometric and compositional imbalanced regions.
Most fibers and fibrous products used in composites are coated with sizings, binders, and/or finishes that serve multiple purposes, including facilitating handling, protection of the fibers from compaction and process induced damage, aiding in compatibility and wetting of the fibers by the resin, and overall enhancement of the composites performance.
Several dry unidirectional tape products utilize a carbon web of unidirectional carbon fibers that has been thermally or adhesively bonded onto a carrier fabric or scrim to support the unidirectional carbon fibers. Several commercial versions are available from V2 Composites, Sigmatex and other textile producers. The limitations of these current products lies in the inability to slit and apply these products via an automated lay down process without deforming and fraying the edges.
In other conventional materials such as the NCF textile (non-crimp fabric), the unidirectional (UD) fiber tows are held together by stitching threads crossing over several carbon tows. In some occasions, very fine fibers are laid across the cross-web direction to provide more lateral stability to the UD fiber tows. In this case, the tows are not spread out and inter-tow gaps as wide as 2 mm exist. Saertex and Sigmatex supply this type of products.
Another conventional method of forming a dry unidirectional tape is the technique comprising spreading a web of fibers and holding the spread fibers with a binderized fine threads usually made of epoxy coated glass threads or polyester or polyamide threads with low heat activation point, running across the width of the tape and holding the spread fibers together. The holding threads are not woven with the web fibers but deposited on the top and/or bottom faces of the web. In this type of product, web fibers are usually well spread out leaving very little tow definition and inter-tow gaps, similarly to standard spread tape produced on prepreg tape machines.
It is believed that none of the state of the art binder compositions or material solutions satisfies the physical, thermo-mechanical and process requirements for the production of dry, fibrous materials that are suitable for used in Automated Tape Laying (ATL) and Automated Fiber Placement (AFP) to form preforms for subsequent resin infusion in composite part manufacturing.